Advances in optically nonlinear materials and single mode fiber technology have led to a renewed interest in integrated optics. For coherent communication fiber systems, integrated optics offers the possibility of an entirely monolithic implementation of narrow linewidth lasers, modulators, detectors, frequency shifters and optical switches. With III-V semiconductors optical functions and associated electronics for drivers and detectors can be on the same opto-electronic chip. Recent advances in nonlinear integrated optics also hold promises for applications in all-optical processing and interfacing of fiber signals. Power dependent nonlinear couplers, nonlinear distributed feedback gratings, optically tunable filters, bistable integrated gratings and logic gates are all possible applications of integrated optics in communication systems resulting from a better understanding of nonlinear guided mode behaviour. New organic (such as liquid crystals) o semiconductor materials (e.g. MQW: multiple quantum wells) in an integrated optics context may provide the properties needed to make all-optical processing viable in the next generation devices.
Several nonlinear switches using bistable devices, some to be used as logic gates, have been demonstrated in the past. Their use for the elimination of conversions between electrical and optical signals in fiber optic communications systems is of great interest and is driving research in novel nonlinear materials. To date, most of the devices demonstrated are based on highly engineering materials and are, unfortunately, also wavelength and temperature sensitive. Silicon has been popular in the past as a substrate for other types of optical waveguides but was largely neglected as the guiding medium itself, apart from some early work at 10.6 .mu.m. Soref and Lorenzo (J. of Quantum Electronics QE-22, p. 873, 1986) recently demonstrated multimode silicon waveguides for use in the near infrared at wavelengths of use in long distance fiber optics and although they mentioned the possibility of optically controlling the waveguide properties, they have concentrated on the electrooptical aspects. They also pointed out several advantages in using silicon for integrated optics. In the present inventor's copending U.S. patent application No. 07/079,767 filed July 30, 1987 now U.S. Pat. No. 4,776,658 issued on Oct. 11, 1988, fiber optic modulators are disclosed in which an optically nonlinear material, e.g. silicon, is provided between a pair of single mode fiber optics defining a fiber-to-fiber mode coupling having a predetermined coupling factor. A control light from a control fiber optic modifies the coupling factor of the nonlinear material, thus modulating the transmission of the carrier light. However, the non-linear material used therein does not form a waveguide. Furthermore, the operating principles are entirely different from those described here.